Batteries to be installed in motor vehicles are used as a source of energy in a vehicle when the engine, and hence the alternator is not running. For example, when the engine speed is slow or the engine is not running, the battery works to provide a voltage of the battery to vehicle loads. On the other hand, when the engine is running, the alternator works to supply an output voltage thereof to both the vehicle loads and the battery, thus charging the battery.
Charge control devices for batteries are therefore designed to control the state of charge (SOC) of a battery based on all operating states of a motor vehicle so as to stably supply electric power to vehicle loads and charge the battery.
The SOC of the in-vehicle battery varies because of various factors including, for example, driver-installed accessories, the use environment of the motor vehicle, and the driver's driving-behavior. The use environment of a motor vehicle represents information of how the motor vehicle is normally used by drivers. For example, the use environment of a motor vehicle represents information of the normal use of the motor vehicle, such as commuting, shopping, or long-distance transport on an expressway.
The variation in the SOC of a battery makes it difficult to properly control the charge of batteries to be installable in various motor vehicles on the basis of common programs and data required to execute the battery-charge control.
On the other hand, some types of engine control systems are disclosed in Japanese Patent Application Publications No. H06-272611 and No. H07-119538. In the engine control systems of these types, a nonvolatile memory is installed. In the nonvolatile memory, programs and data required to control an engine are stored in advance. The nonvolatile memory is designed to be externally rewritable.
After such an engine control system is placed on the market, it is possible to rewrite the control programs and data stored in the nonvolatile memory.
In order to implement the external rewriting, the engine control system has installed therein a dedicated communication circuit for communicating with a memory writer as an example of external devices. Connectors have also been installed in the respective dedicated communication circuit and the memory writer for specifically connecting therebetween. Furthermore, a wire is required to connect between the dedicated communication circuit and the memory writer.
These additional components required for the engine control system to communicate with the memory writer may increase the scale of the engine control system, resulting an increase in cost thereof.